Snowmaking machines of the ducted-fan type are well known and described in such patents as U.S. Pat. Nos. 4,004,732; 4,214,700; 4,222,519; and 4,493,457. In general, ducted-fan snowmaking machines include an axially-elongated duct or cowling supported on a portable carriage to permit movement of the machine to various locations. An impeller is rotatably mounted in the duct and rotated in a direction and at a speed to generate a substantially unidirectional air stream at atmospheric pressure for discharge from one end of the duct. Into the air stream is introduced a quantity of water by means of nozzles positioned about at least a portion of the discharge end of the duct. A nucleating or seeding nozzle is also located at the discharge end of the duct for introducing a mixture of water and compressed air into the stream to facilitate nucleation of snow crystals in the stream.
Ducted-fan type snowmaking machines provide numerous advantages over compressed air type snowmaking machines which had been used previously. In particular, ducted-fan type snowmaking machines provide a lower operating cost and have a lower noise level of operation than the compressed air type machines. The lower noise level exhibited by the ducted-fan snowmaking machines is a highly desirable feature since snowmaking machines often are used in proximity to inhabited areas, such as condominiums, hotels, and the like, where noise levels should be maintained as low as possible to avoid disturbing the inhabitants, especially during nighttime hours when they are attempting to relax or sleep.
For purposes of illustration, noise levels of various commercially available ducted-fan snowmaking machines (at distances of 20 feet and 66 feet in front of the machine discharge end) have been found to be in the range of approximately 71 to 84 dbA and 70 to 78 dbA (logarithmic scale decibel average), respectively. In contrast, noise levels of various commercially available compressed air machines have been found to be in the range of approximately 100 to 106 dbA and 91 to 94 dbA, respectively, at the same distances (20 feet and 66 feet) in front of the discharge end. As is apparent, the ducted-fan snowmaking machines offer substantially reduced noise levels of operation as compared to the compressed air machines. Even so, operators of ski and other facilities using snowmaking equipment on a frequent basis, especially near inhabited areas, continue to express a strong desire for snowmaking apparatus having still lower levels of noise.
It is an object of the present invention to satisfy this desire by providing improved ducted-fan snowmaking apparatus and methods wherein a particular noise level of operation can be purposefully and controllably selected with reference to the proximity of the apparatus to an inhabited area and provide environmentally acceptable noise levels.